The invention relates to a relay valve arrangement which can be used in the ABS system of a vehicle.
A relay valve arrangement of this type is marketed by WABCO Westinghouse Fahrzeugbremsen GmbH under Device No. 72 195 020 0. This relay valve arrangement is designed to carry out three modes of operation during ABS-controlled braking: pressure increase, pressure hold, and pressure decrease. The relay valve arrangement includes an inlet chamber for a working pressure fluid (hydraulic or pneumatic), a work chamber, an outlet through which the working pressure fluid is delivered to a brake cylinder, an outlet to exhaust, and a combined inlet-and-outlet valve which includes a relay piston. The position of the relay piston determines which mode of operation is carried out. The relay valve arrangement further includes a control chamber which controls the position of the relay piston. The control chamber is aerated with a control pressure fluid through a solenoid-actuated inlet valve and deaerated through a solenoid-actuated outlet valve.
In a relay valve arrangement of this type, it may occur that the solenoid-actuated outlet valve does not reach its open position to deaerate the control chamber rapidly enough in the pressure holding mode (working pressure inlet and outlet valves of the relay valve closed) when the pressure drops rapidly in a control pressure circuit which delivers the control pressure fluid to the control chamber.
The delayed response of the solenoid-actuated outlet valve is due to the fact that an electronic regulating circuit interacting with the relay valve arrangement of a vehicle equipped with an ABS regulating system is unable to recognize immediately when the driver of the vehicle lifts his foot from the brake pedal and thereby deaerates the control pressure circuit leading to the solenoid-actuated inlet valve of the relay valve arrangement in order to terminate the braking process. Only when the braking pressure supplied by the relay valve arrangement to the brake cylinders on the basis of the control pressure still present in the control chamber causes further deceleration of the vehicle wheels and when locking tendencies of the vehicle wheels are recognized by the electronic regulating circuit does said electronic regulating circuit transmit a signal to the solenoid-actuated outlet valve. The latter then assumes its open position and the control chamber is deaerated. The relay piston then brings the outlet valve of the combined inlet-and-outlet valve of the relay valve arrangement into open position and the brake cylinders of the vehicle are deaerated.
The consequences of the delayed response of the solenoid-actuated outlet valve are a delayed start of pressure drop in the control chamber and thereby also a delayed reaction of the relay piston, resulting in a delayed braking pressure drop in the brake cylinders, and this in turn delays a desired end of the braking process.
In order to deal with this circumstance, a return valve is installed between the control pressure circuit and the control chamber, said return valve being held in closed position when control pressure is present in the control pressure circuit and which is brought by the pressure in the control chamber into its open position when the pressure drops in the control pressure circuit. As the delivery of control pressure to the control pressure circuit via a control pressure coupling drops, the pressure also begins to drop in the control chamber as a result of this measure even before the solenoid-actuated outlet valve opens. Thus, dead time no longer occurs between pressure drop in the control pressure circuit and the pressure drop in the control chamber.
In the known relay valve arrangement, the return valve is installed in a housing wall between the control chamber and the control pressure circuit (which actually constitutes a channel in this wall) connected to the control pressure coupling.
Such an arrangement of the return valve however requires various costly measures and means. A stepped bore must be provided in the housing wall to receive the return valve. Special retaining means must be provided to hold the return valve in the bore. Special sealing means must also be provided.
In a known relay valve arrangement of this type, it is furthermore required that an armature support be provided for the armature of the solenoid-actuated inlet valve and that the support be designed so that the pressurized fluid (i.e., hydraulic fluid or pneumatic air) be able to reach below the armature in order to accelerate the movement of the armature during the closing process of the solenoid-actuated inlet valve.
It is the object of the instant invention to provide an improved relay valve arrangement of the type discussed in such manner that the arrangement and the design of the return valve are simplified.